An experiment was undertaken to determine from which part of silver belly (Leiognathus splendens) carcasses originate the autolytic enzymes responsible for liquefaction of silage. Findings show that it is important to leave head and viscera present in order to get a satisfactory liquefaction in silage prepared from silver belly using 3.5% formic acid. The storage life of silage produced from various parts of the fish carcasses is also discussed

Jayawardena, K.M.

Poulter, R.G.

Aquatic Commons

Bull. Fish. Res. Stn., Sri Lanka, Vol. 30, 1980, pp. 25-31. 
Studies on the Preparation of Fish SiUlage 
ll. Rate of Liquefaction in different parts of Silver Belly 
By 
K. M. JAYAWARDENA* and R. G. POULTER'! 
Introduction 
In part I of this study to determine the technical and economic feasibility of producing fish silage 
commerciaHyin Sri Lanka (Jayawardena et al, 1980), the quality and storage Hfe of silages made from 
silver belly of different initial quality and with different acids was investigated. The present paper 
presents the results of an experiment to determine from which part of th~ fish carcass the autolytic 
enzymes responsible for liquefaction mainly originate. The storage life of silages produced from 
various parts of the fish carcass using 3.5% formjc acid is also reported. · 
JVIaterials and Methods 
Fish Samples 
Silver belly (Leiognathus splendens) locally known as "Karall'a" were used" Tb.ey were caught 
in November, 1978 during prawn trawling operations off the Jaffna coast. The :fish were iced on 
landing and transported to Colombo where they were frozen. Mter 6 weeks of storage at- 25°C 
the fish were thawed, the carcass composition was determined and silages produced from the various 
parts. 
Carcass Composition 
Fish (25) were selected at random and the body length and weight d.ete:rminoo. Each fish was 
then Cilrefully dissected and the parts, i.e. flesh, head, frame, skin, viscera. and fins weighed separ-
ately. The carcass composition(% w/w) was calculated. 
Preparation of Silage 
Table 1 gives details of the carcass parts used to produce the 6 siJage samples. The various 
parts for any one sample were mixed together in the same proportion as they occur in whole fish and 
approximately 1 kg was ground in an electric mincer. Formic acid, 3.5% v>!}w of a,n 8 5% w /v solution, 
\'Fas added to the mince and thoroughly mixed by hand. The samples were stored in 2 Htre plastic 
containers with loose fitting lids at an ambient temperature of28°C to 30°C. 
Analytical rnethods 
Water, ash, fat, total nitrogen, crude protein and pH were detenll'llmed as described previously 
(Jayawardena et al. 1980). 
,~ Institute of Fish Technology, C:rowisland, Mattakkuliya, Colombo 15. 
t Seconded f:rom the Tropical Products Institute, 56/62, Gray's Inn Road,. London, EJnglan,,JL 
25 
26 STUDIES ON THE PREPARATION OF FISH SILAGE-II 
Degree of Autolysis 
The increase in autolysis with time in the silage samples was estimated in 2 ways. Firstly, 
the degree of liquefaction was determined by centrifuging the samples in an IEC bench centrifuge at 
3,000 rpm for 30 minutes. The supernatants were carefully removed and weighed. The weight of the 
liquid phase was expressed as a percentage of the total weight of sample. Secondly, the non-protein 
nitrogen (NPN) content of the silage samples was measured. Protein nitrogen in 2 g samples was 
precipitated by adding 50 ml of 10% tri-chloroacetic acid and removed by filtering. The amount of 
NPN contained in 20 ml of the :filtrates was determined using the standard micro-kjeldahl procedure 
(Pearson, 1970) and expressed as a percentage of the total nitrogen. 
Results and Discussion 
The mean weight of25 silver belly wiJ.S 8.1g (range 5.8 to ro .5g) and the mean length was 6.9 em (range 
6.0 to 8.0 em). The carcass and chemical composition (means of duplicate analyses) of the fish are 
given in Table 2. 
Silver belly is a small, mesopelagic fish with a low fat content in the flesh. However, the fat 
content of the viscera is relatively high as is the ash content. Up to 60% of the latter may be sand 
(Etoh, 1979). 
The appearance and odour of the silage samples ~-t 1, 2, 11 and 64 days after producton is 
given :in Table 3. The silage made from flesh only became putrid after 10 days and the silage containing 
viscera showed growth of yellow moulds after 55 days. The other samples remained in an acceptable 
condition for 64 days. 
Table 3 also shows that there were significant differences in the rate of liquefaction of 
the samples. The whole fish liquefied most rapidly followed in tum by the sample containing viscera, 
ihe sample containing heads, the sample containing skin, the sample with flesh/frames/fins and finally 
by the sample containing only flesh. 
The same pattern is clearly sho·wn in Figure 1 which gives the changes in the NPN contents 
of the samples. 
Together these results give an indication of the concentration and activity of the proteolytic 
enzymes contained in the various carcass parts. It is these autolytic enzymes rather th;:m the added 
fonnicacid which breakdown the structural proteins into smaller water soluble units and brings about 
the liquefaction of the samples. It appears that in order to obtain a liquid product it is necessary to 
have viscera and/or -heads present. 
The NPN content of the :flesh-only silage sample was quite lovv until the 1 Othday after production 
when there was a sudden increase. This coincided with the occurrence of off putrid odours in the 
sample and wa.s probably due to the production of low molecular weight nitrogenous compounds such 
as amines. 
Figure 2 shows the changes in the weight of the aqueous phase of the samples during storage. 
Although the pattern is not so distinct c.s in T?.ble 2 of Figure 1, the results show that silage s;:.mp-
les containing viscera or heads had a larger aqueous phase than the samples without these parts. 
No aquem.1.<s phase at an could be sep~t:rated from the flesh-only sample by centrifuging. 
In ge:~1eral, it WP-s extremely difficult to obtain a clear separation ofthe aqueous and sedimentary 
phases by centrifuging for 30 minutes at 3,000 rpm. Indeed, there were often more than 2 phases 
ii.pparent and the nature of these phases changed as the period of storage increased. Initially the 
K. M. JAYAWARDENA AND R. G. POULTER 27 
aqueous phase consisted of a dear fluid but after 2 days this liquid became more viscous and less easy 
to separate from the gel-like sedimentary phase. This accounts for the initial drop in the curves given 
in Figure 2. On further storage the aqueous phase increased again. After a few days however, 4 
phases were to be seen after centrifuging ; a lipid layer, a clear aqueous layer, a thick viscous layer 
containing suspended solids and a layer containing pieces of bone, connective tissue etc. There was 
no real margin between layers 2 and 3 which led to a certain amolmt of variability in the results. 
Ta b]e 4 gives the chemical composition oft he silages 4 weeks after production and their aqueous 
phase 9 weeks after production. The nitrogen content, rather than crude protein content, is given since 
the conversion factor of 6.25 may not be applicable when up to 60% of the nitrogen appears in the 
NPN fractions. There was very little difference in the chemical composition of the silages or theie 
aqueous phases other than the fact that the sihtges containing heads had a rather high ash content. 
Table 5 gives the pH of the silages at 1, 2, 11, and 64 days after production. As reported earlier 
(Jayawardena et al., 1980) the pH of formic acid silage rises slightly after production. A small rise 
is acceptable but a large rise indicates spoilage of the sample ; for example the :flesh- only silage 
which went putrid had a pH of 8.2 and the silage containing viscera which showed mould growth had 
a pH of 4.6. 
Conclusions 
1. In order to get a satisfactory liquefaction in silage prepared from silver beUy using 3.5% formic 
acid, it is necessary to have the viscera or heads present. Exclusion of these parts means 
that liquefaction, if it does occur, is very slow and that even mixing of the acid is difficult to achieve. 
This win result in the silage being more susceptible to microbiological spoilage. 
2. Provided it may be mixed in e~sily, 3.5% formic acid is sufficient to prevent spoilage for up 
to 2 months in silages produced from good quality fish. However, such silages may be susceptible to 
mould attack, particularly on prolonged storage. 
3. Measurement of changes in NPN content is the best objective method for assessing 
changes in the degree of liquefaction and autolysis. 
4. Measurement of pH changes gives a good indication ofwheti1er the quaMy of the silage is 
deteriorating. 
ACKNOWLEDGEMENTS 
The assistance of the technical staff of the Institute of Fish Technology is gratefully acknovvledged. 
REFERENCES 
EroH, S. (1979) 
Personal comm1llllication. 
PAYAWARDENA, M., Vn.LADSEN, A., AAGAARD, J., GUNERATN'E, Q., POULTER, R. G. (1980) 
Studies on the preparation of fish silage : (1) Effect of quality of raw material and type of add. Bull. Fish. ReJ:~ 
Stn., Sri Lanka, Vol. 30, 1980,pp.17-23. 
JEARSON, D, (1970) 
The chemical analysis of foods, 6th edi.tion, Churchill, London, 604 pp. 
28 STUDIES ON THE PREPARATION OF FISH SILAGE_;.;II 
TABLE 1 
DJETA.JILS OlF CARCASS PARTS lN TilE SILAGE SMJPLES 
Sample Carcass Parts 
r- ----. 
~ Hesh Frame Fins Viscera Head Skin 
2 Hesh Frame Fins Viscera 
:J Hesh Frame Fins Head 
4 Hesh Frame Fins Skin 
5 Flesh Frame Fins 
6 Hesh 
TABLE 2 
CA.RCASS AND CHEl\illCAL COMPOSffiON OF SILVER BELLY 
-whole fish 
Flesh 
Head 
Frame 
Skin 
Viscera 
FiD"S 
Sampf.e 
Silage Samples 
Whole fish 
Flesh /Frame /Fins [Viscer~. 
Fiesh[Frame{Fins[Head 
HeshfFramejFinsfSlldlm 
Flesh /Frame/Fins 
Flesh 
Carcass 
Composition 
%(wjw) 
100 
36.9 
22.2 
16.6 
6.2 
6.1 
1.5 
AJP'PEAlRf-'u'\fCE AND 
1 
Dark grey, 
Moist 
Light grey, 
Moist 
Dark grey, 
Slightly 
moist 
Grey, 
Ve1y slightly 
moist 
Light grey, 
Dry 
Off whi.te, 
Dry 
Crude 
Water Ash Fat Protein NPN 
% (wfw) % (wjw) % (wjw) % (wjw) %(w{w) 
74.2 5.5 3.0 17.6 
75.3 1.1 2.7 22.7 0.1 
69.4 10.0 5.3 21.8 0.1 
59.8 12.8 5.8 23.1 0.2 
67.8 2.0 6.7 25.0 0.2 
61.3 13.7 9.8 13.1 0.2 
54.9 ')1 " -.•. ;) 1.2 21.0 0.1 
TABLE 3 
ODOUR OF SILAGE SAMPLES 
Time of Storage (Days) 
~ 
2 11 64 
Dark grey, Dark grey, Dark grey, 
Semi-liquid Liquid Liquid, 
Malty faci.dic 
odour 
Light grey, Light grey, Yellow moulds, 
Semi-liquid Liquid Liquid, 
Strong mouldy 
odour 
Dark grey, Dark grey, Dark grey 
Semi-liquid Liquid Liquid, 
Fresh acidic 
odour 
Grey, Grey, Grey, 
Dry paste Slightly moist Slightly moist 
paste paste 
Acidic odour 
Light grey, Light grey, Light grey. 
D1y paste Dry paste Moist paste, 
Acidic odour 
Off white, Creamy Discarded 
Dry brown, 
Moist, 
Putrid odour 
K •. M• JAYAWARDENA Al'i'D R, G. POULTER 
TABLE 4 
CHEMICAL COJ\'IPOSr.f..I:ON OF WHOLE SILAGE SAJ\'IPLES FOUR WEEKS .AFTER PRODUCTION 
Al'i'I) SILAGE AQUEOUS PHASES NINE WEEKS .AFTER PRODUCTION 
Silage Sample 
vVhole fish 
Flesh/Frame{FID.s/Viscera 
Flesh/Frame/Fins/Head 
Flesh/Frame/Fins/Skin 
Flesh/Frame/Fins 
Flesh 
( 
.. 
Water Ash 
% (wfw) % (w/w) 
r-
Whole Aqueous Whole Aqueous 
Sample Phase Sample Phase 
72.1 83.7 7.4 2.9 
74.4 83.9 5.2 2.7 
71.1 85.2 7.2 2.8 
74.0 86.2 4.0 2.5 
74.4 86.6 4.5 2.4 
No aqueous phase-sample discarded after 11 days 
TABLE 5 
CHAJ.'l"GE IN pH OF SILAGE SAl'VIPLES "WIIH 'IllVIE 
Time of Storage (Days) 
Silage Sample 
1 2 11 
'Whole fish 3.6 3.8 3.8 
Flesh/Frame/Fins/Viscera .. 3.6 3.8 3.8 
Flesh/Frame/Fins/Head .. 3.6 3.8 3.8 
Flesb.fFrame/Fins/Skin. 3.5 3.7 3.7 
Flesb.fFrame/Fms 3.5 3.7 3.7 
Flesh 3.1 3.9 8.2 
Nitrogen 
% (wfw) 
Whole Aqueous 
Sample Pita$(! 
2.8 1.8 
2.9 1.9 
2.7 ),6 
3.1 1.1 
3.0 1.6 
64 
4.0 
4.6 
4.0 
3.8 
3.8 
30 STUDIES ON THEPREPARA'IION.OF FISH SILAGE-II 
50 
40 
f\ 
r; 
<) 
I)">, 
0 
,._ 
<-' 
.~ 
·' 
-;; 
-<6 
..., 
't 
~<.. 30 
~ 
----
z: 
l 
z 
20 
TIM.E,. OF STORAGE {da..ys) 
Figure 1.- Change in NPN content(% w/w of total nitrogen) of silages during storage. \Vhole fish (0), sample 
containing viscera (e), sample containing heads (0), sample containing skin sample with flesh, 
fraJIDe and fins (6), flesh only sample 
K. M. JAYAWARDENA AND R. G. POUL'IJER 
Figure 2 
35 
;...--.. ~-
" en 25 
-:l 
_!II 
c 
..s: 
Jt 
'3 
~ 3' 
c 20 
_/ ____ .-----
' 
----· 
' 
' 
3! 
/ 
10 ~~m.--.-~~m>~W®~~~~~~~~~~~.-m.~._._._._._ 
0 10 20 30 Lj.l) 50 60 70 
TIME OF STOR!>GE (do.ys) 
I'igmre 2- Change in weight of aqueous phase (% w/w of whole silage) of silages during storage. 
sm:nple containing viscera ( • ), sa:mple containing heads (0), sa:mple containing skin 
flesh, frame and :fins (U.) 
4--A 50175 (80/06) 
Whole fish (0} 
sample with 


Studies on the preparation of fish silage. 2. Rate of liquefaction in different parts of silver belly

http://aquaticcommons.org/17273/1/NARA30_025.pdf

Studies on the preparation of fish silage. 2. Rate of liquefaction in different parts of silver belly

Abstract

Similar works

Full text

Available Versions

Aquatic Commons